[COMMITTED 052/101] gccrs: Allow const and async specifiers in functions

[arthur . cohen]

From: Pierre-Emmanuel Patry <pierre-emmanuel.pa...@embecosm.com>

We need to account for const specifiers in async parsing as const
can be used in the syntax before the async keyword.

gcc/rust/ChangeLog:

        * parse/rust-parse-impl.h (Parser::parse_vis_item): Allow parsing async
        items in const.
        (Parser::parse_async_item): Account for const offset during async
        lookahead.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.pa...@embecosm.com>
---
 gcc/rust/parse/rust-parse-impl.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/gcc/rust/parse/rust-parse-impl.h b/gcc/rust/parse/rust-parse-impl.h
index a1ad4f11993..acceec302a2 100644
--- a/gcc/rust/parse/rust-parse-impl.h
+++ b/gcc/rust/parse/rust-parse-impl.h
@@ -1383,6 +1383,8 @@ Parser<ManagedTokenSource>::parse_vis_item (AST::AttrVec 
outer_attrs)
          return parse_const_item (std::move (vis), std::move (outer_attrs));
        case UNSAFE:
        case EXTERN_KW:
+       case ASYNC:
+         return parse_async_item (std::move (vis), std::move (outer_attrs));
        case FN_KW:
          return parse_function (std::move (vis), std::move (outer_attrs));
        default:
@@ -1445,7 +1447,9 @@ std::unique_ptr<AST::Function>
 Parser<ManagedTokenSource>::parse_async_item (AST::Visibility vis,
                                              AST::AttrVec outer_attrs)
 {
-  const_TokenPtr t = lexer.peek_token ();
+  auto offset = (lexer.peek_token ()->get_id () == CONST) ? 1 : 0;
+  const_TokenPtr t = lexer.peek_token (offset);
+
   if (Session::get_instance ().options.get_edition ()
       == CompileOptions::Edition::E2015)
     {
@@ -1456,7 +1460,7 @@ Parser<ManagedTokenSource>::parse_async_item 
(AST::Visibility vis,
                     "to use %<async fn%>, switch to Rust 2018 or later"));
     }
 
-  t = lexer.peek_token (1);
+  t = lexer.peek_token (offset + 1);
 
   switch (t->get_id ())
     {
-- 
2.42.1